Magnetron output coupler



v Jan. 10, 1961 J.- R. M. VAUGHAN MAGNETRON OUTPUT COUPLER Filed March 4, 1959 INVENTOR: JAMES R. M. VAUGHAN %D HIS ATTORNEY.

MAGNETRON OUTPUT COUPLER James Rodney M. Vaughan, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Mar. 4, 1959, Ser. No. 797,067

4 Claims. (Cl. 315-3953) My invention relates to magnetrons and pertains more particularly to new and improved magnetron output coupling means.

Many magnetrons include output coupling systems comprising a radially extending waveguide output and a slot or other aperture extending from a cavity resonator in the anode structure through the envelope wall of the device to the waveguide output. Additionally, the waveguide is generally fitted with a dielectric window which is substantially transparent to radiant energy at the operating frequencies of the device. In such devices failures of the windows after relatively short operating lives and as by cracking has been caused by the deposition and accumulation of conductive material on the inner surface of the Window. This material emanates from the cathode or from the anode vanes and has been found to accumulate particularly on a bar-shaped central region of the window corresponding generally in area to the cavity slot in the envelope wall through which a straight line of sight exists between the window and the cathode or vane tips.

Heretofore, efforts have been made to shield the window or to avoid deposition of conductive material from the cathode on the window by forming the mentioned cavity slot in the envelope wall in a skewed or oblique position relative to the axis of the coupling device or by interposing a masking element between the slot and window, thus to avoid a direct line of sight between the slot and window. However, in many applications the inclusion of an oblique slot in the envelope wall is structurally or physically undesirable. Additionally, the use of a masking element introduces problems in relation to adjustments and locations thereof relative to other elements to avoid undesirable effects on the impedancematching characteristics of the output coupling device; and, therefore, the use of masking elements is also generally undesirable, especially in production tubes.

Accordingly, a primary object of my invention is to provide a new and improved output coupling system for a magnetron and including an energy transmission window and improved means for avoiding damage to the window by deposition thereon of conductive material emanating from the cathode of the magnetron, thus to increase window life and, in turn, to increase the continuous operational life of the magnetron.

Another object of my invention is to provide a new and improved waveguide output transformer which is substantially a quarter wave length long at the operating frequency and includes self-contained means effective for avoiding straight line transit of material therethrough.

Another object of my invention is to provide a new and improved output coupling device including an improved transformer adapted for avoiding deposition of conductive material on an energy transparent window in one end of the device without adversely affecting the electrical characteristics of the transformer and without requiring special adjustment of elements to obtain desired electrical operation of the device.

Another object of my invention is to provide a new and improved waveguide output transformer which is simple in construction, easily manufacturable and readily substitutable for less effective coupling devices employed in standard magnetron constructions.

Further objects and advantages of my invention will become apparent as the following description proceeds and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming part of this specification.

In carrying out the objects of my invention I provide a magnetron including a radially extending waveguide output in the end of which is sealed a dielectric energy transparent window, a radially extending slot interconnects a cavity resonator in the magnetron with the wave guide output and an impedance-matching transformation is made between the resonator and waveguide by a transformer which extends in the waveguide a distance substantially a quarter wave length long at the center frequency of the magnetron. The transformer comprises a pair of spaced conductor vanes including opposed surfaces defining a passage from the slot toward the window including a double right angle bend and which surfaces diverge at the ends of the vanes adjacent the window. The transformer is thus also effective for preventing raight line deposition of conductive material from the cathode on the window, thereby to avoid damage to the window from accumulations of such material.

For a better understanding of my invention reference may be had to the accompanying drawing wherein:

Figure 1 is a fragmentary and somewhat schematic sectional illustration of a magnetron incorporating my invention; and

Figure 2 is an enlarged fragmentary perspective view illustrating in detail the various features of my improved transformer.

Referring to Figure 1 of the drawing there is shown a magnetron comprising a cathode I mounted centrally of a plurality of cavity resonators 2. The cathode 1 is illustrated in the drawing by way of example only and may comprise any one of the many types generally available in the art and employable in magnetrons of similar construction. Additionally, the cathode contains a required energizing element (not shown) such as a heater filament. Also provided and not shown are suitable lead-in conductors and cathode support structure.

The cavity resonators 2 can comprise a plurality of radially extending conductive elements or vanes 3. secured at the outer edges to a cylindrical anode block 4 of conductive material. The anode block 4 can be centrally disposed in a cylindrical conductive outer wall member or envelope 5. The ends of the member 5 are covered with end plates (not shown) which complete the envelope of the device and adapt it for evacuation. Additionally, the end plates can carry concentric pole pieces adapted for concentrating a magnetic field coaxially in the device transverse the electric field between the cathode and anode structure thus to enable magnetron operation in the well known manner.

The particular details of the magnetron described to this point are well known and any desired magnetron may be substituted therefor.

The output coupling system which comprises my invention is illustrated in both Figures 1 and 2 and will now be p with a frame structure generally designated 7 in which is sealed a transversely extending energy transparent window 8 which can be advantageously formed of ceramic or any other suitable dielectric material. While the particular waveguide shown is of circular cross section, it is to be understood that the waveguide can be of any desired crosssectional configuration.

The slot 9, which is preferably rectangular, opens into the waveguide 6 and is in register and alignment with the central passage of an impedance transformer generally designated 10.

The transformer 10 is substantially a quarter wave length long at the center frequency of the operating frequency band of the magnetron and comprises a pair of conductive vanes 11 and 12 which are supported from diametrically opposed sides of the waveguide 6, as by being brazed to the walls thereof, and are spaced to provide the aforementioned energy passage. Additionally, the vanes 11 and 12 are shaped to provide a double right angle jog or indirect path between the slot 9 and the window 8. Thus, conductive material emanating from the cathode or anode vanes and tending to be transmitted along a straight line path through the resonator cavity 2 and the slot 9 and toward the window 8 is intercepted by interposed portions of the transformer to prevent deposition of such material on the window. As pointed out above, accumulation of conductive or lossy material on the window 8 tends to cause failure thereof, as by cracking. Additionally, the vanes 11 and 12 are shaped to provide opposed diverging surfaces designated 13 and 14, respectively, at the outer ends of the transformer vanes for assisting in effecting the desired impedance matching between the resonator and the waveguide.

More specifically, the means 11 and 12 comprise blocks of metal which can advantageously be copper and which are dimensioned and shaped for being positioned and secured in the inner end of the waveguide with the outer surface conforming to the contiguous inner surface portions of the waveguide and having fiat parallel surfaces 15 and 16. The surfaces 15 and 16 comprise elongated straight surfaces and together define an elongated straight passage coaxially aligned with the waveguide and in register with the aperture 9. At the ends of the surfaces 15 and 16 are located surfaces 17 and 18, respectively, which extend at right angles to the surfaces 15 and 16 and together define a transverse right angle bend or jog in the mentioned energy passage and which provide communication between the straight portion of the passage and that portion defined by the diverging surfaces 13 and 14. This arrangement of surfaces results in the diverging surfaces being located about an axis offset or laterally spaced from the longitudinal axis of the waveguide. In summary, and as illustrated in the drawing, the various opposed surfaces of the transformer vanes define a central slot through the transformer which extends for a portion of the transformer and then jogs or makes a right angle bend before opening divergently at the end of the transformer and from a position which is offset in respect to the center of the transformer or longitudinal axis of the transformer and waveguide section.

My above-described coupling system is particularly adapted for obtaining several advantages. For example, it is readily interchangeable with currently employable output couplers and its use requires no changes in the tube structure such as cutting of skewed slots in the anode block. Further, my system requires no additional elements such, for example, as masking elements, the introduction of which in a coupling device necessitates careful adjustments of the relative positions of the several elements comprising the transformer to minimize adverse effects on the electrical characteristics of the device. Still further, my invention enables the provision of a quarter wave length long transformer including only a pair of vanes as the essential elements in a waveguide and which vanes cooperate to avoid straight line deposition of material from the cathode on the waveguide window without also introducing undue electrical effects or requiring adjustments for desirable operation. Additionally, my structure is simple in construction requiring a minimum of parts and, accordingly, is attractive in the manufacture of high-production quantities of magnetrons.

While I have shown and described a specific embodiment of my invention I do not desire my invention to be limited to the particular form shown and described, and I intend by the appended claims to cover all modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An output coupling system comprising a resonator, a waveguide wherein coupling is effected between said resonator and waveguide by an aperture interconnecting said resonator and waveguide and coaxial with said waveguide, an energy transparent dielectric window sealed across said waveguide, and a pair of impedance-matching transformer vanes within said waveguide between said aperture and window and extending from diametrically opposed inner surfaces of said waveguide toward each other, said vanes extending longitudinally from said aperture toward said window for a distance of substantially only a quarter wavelength long at the center frequency of said system, the opposed surfaces of said vanes defining an indirect energy passage between said aperture and window effective for transmitting energy from said resonator to said window and preventing straight line transit of conductive material from said aperture toward said window, thereby to avoid damage to said window by accumulations of conductive material thereon.

2. An output coupling system comprising a resonator, a waveguide wherein coupling is effected between said resonator and said waveguide by an aperture interconnecting said resonator and waveguide and coaxial with said waveguide, an energy transparent dielectric window sealed transversely in said waveguide, and a pair of impedance-matching transformer vanes within said waveguide between said aperture and window and extending from diametrically opposed inner surfaces of said waveguide toward each other, said vanes extending longitudinally from said aperture toward said window for a disstance substantially only a quarter wave length long at the center frequency of said system, the opposed surfaces of said vanes defining a longitudinally extending energy passage including parallel spaced walls and a right-angle bend adjacent said aperture and diverging walls opposite said aperture, whereby energy is effectively transmitted from said resonator to said window and straight line transit of conductive material from said aperture toward said window is prevented to avoid damage to said window by accumulations of conductive material thereon.

3. A magnetron comprising an evacuated envelope, a centrally disposed cathode in said envelope, an anode structure in said envelope including a plurality of radially extending elements defining a plurality of cavity resonators encompassing said cathode, an output waveguide extending radially from said envelope, a radially extending aperture in said envelope interconnecting said waveguide and one of said resonators and aligned with the longi tudinal axis of said waveguide, an energy transmitting dielectric window sealed transversely in said waveguide, and an impedance-matching transformer extending in said waveguide from said envelope comprising a pair of conductive vanes supported in spaced relation, said vanes including opposed end surfaces diverging from an axis offset with respect to said longitudinal axis of said waveguide, and said vanes including inner opposed surfaces defining a passage including a straight portion aligned with said aperture and said axis of said waveguide and including an abrupt bend toward the axis of said diverging surfaces, whereby energy is effectively transmitted from said resonator toward said window, and straight line transit of conductive material from said cathode and through said resonator and aperture toward said window References Cited in the file of this patent UNITED STATES PATENTS 2,765,423 Crapuchettes Oct. 2, 1956 2,817,790 Kline et a1. Dec. 24, 1957 2,836,764 La Rue May'27, 1958 

